Telegraph system



' April 8, 1941. J.T. NEISWINTER TELEGRAPH SYSTEM 3 Sfieets-Sheet 1Filed Dec. 22, 1939 mvmyon JZUl ewwzner ATTO R NEY April 1941- J. "l'.NEISWINTER 2.237.498 1 TELEGRAPH SYSTEM Filed Dec. 2.2, 1959 sSheets-Sheet 2 ATTORNEY April 8, 1941- J. T. NEISWINTER TELEGRAPH SYSTEMFiled Dec. 22, 1939 3 Sheets-Sheet 3 INVEN'TOR JZ/Vewwamter BY V IATTORNEY Patented Apr. 8, 1941 UN lTED STATES I PATENT OFFICE TELEGRAPHSYSTEBI 7 James T. Neiswinter, North Olmstead, Ohio, as-

signor to American Telephone and Telegraph Company, a corporation of NewYork Application December 22, 1939, Serial No. 310,649

6 Claims.

This invention relates to telegraph systems and to repeaters fortelegraph systems. More particularly, this invention relates torepeaters for telegraph systerns in which two-Way communication may becarried on over a single line circuit.

The repeaters included in the telegraph system of this invention areeach capable of sending and receiving signals over a line circuit in onedirection at a time. are connected to each other over a line circuit,each repeater is set up to receive signals coming from the otherrepeater when the system is in an idle condition. During the period ofidleness no battery potential whatever is applied to the line circuit.When a subscribers loop circuit transmits signals to one of therepeaters, that repeater will be rearranged by the first spacing impulseso that the repeater may relay the sig- When two such repeaters nals tothe other repeater, After a predetermined period of idleness upon theconclusion of signaling, the two repeaters will be rearranged to theidle or receiving condition.

This invention, together with its further objects and features, will bebetter understood from the detailed description hereinafter following;when read in connection with the accompanying drawings, in which Figure1 represents one embodiment of the invention, this figure schematicallyrepresenting a circuit illustrating the principles of the invention;Fig. 2 represents a more detailed embodiment of the invention, and Fig.3 illustrates certain curves used to explain the operation of certain ofthe apparatus of the invention.

Referring to Fig. 1 of the drawings, two repeater stations designated Pand P are shown interconnecting two subscribers loop circuits designatedL1 and L1 which form part of a telegraph system. The apparatus atstation P may be identical with that at station P, correspondingapparatus being designated by the same reference characters except thatthey are primed at station P". Station? includes three telegraph relaysdesignate-d C, S and R, the relay C being a fast operate slow releasecontrol relay, the relay S a sending relay and the relay R a receivingrelay. The apparatus at station P is connected to the apparatus atstation P by a line L, which may have lumped or uniform resistance,lumped resistances designated Z0 and Z0 being shown connected to theinterconnecting line for illustrative purposes. The terminal common tothe two resistances Z0 and Zn" may be connected to ground by a condenserK. The repeater apparatus at stations P and P may be used to relay isignals in opposite directions between the subscribers loops L1 and L1in a manner to be described more clearly'hereinafter.

When the circuit is idle, i. e. when no signals are being transmitted orreceived over the system, the armatures of all of the relays will be ontheir marking contacts m, as indicated in the drawing, Each end of theline L will be grounded and hence no current will be transmitted overthe line L. The circuit connecting the line L to ground at station Pwill include the armature and marking contact m of relay S, the upperwinding of the relay R1, the armature and marking contact m of relay C,the lower winding of relay R and ground. A similar circuit will connectthe opposite end of line L to ground at station P.

While the circuit remains idle, the armatures of the two receivingrelays R and R will be held on their marking contacts by a small currentcirculating through the lower windings of the two relays. This holdingcurrent will emanate from the battery B1 at station P and will flow overthe marking contact in and armature of relay R, the resistor Z1, thelower winding of the relay R and ground. A similar holding circuit,which need not be described, will permit a small current to flow frombattery B1 at station P" through the lower winding of the receivingrelay R at that station.

Assume now that a spacing signal is transmit ted over the loop L1 fromthe subscribers apparatus (at the left) connected to the loop. This maybe accomplished by moving the armature of the key K to its spacingcontact 8. When this occurs the loop circuit L1 will be opened and henceno current will flow from the battery Bu over the loop circuit L1 andthrough the resistor Z2 and through the upper windings of the relays Cand S at station P. The armatures of the two relays C and S will thenclose their spacing contacts 3 under the influence of current flowingfrom battery B1 through the lower windings of relays S and C throughresistor Z3 to ground. Upon the closure of the spacing contact .9 ofrelay S, the spacing battery B12 will be connected to the line L, thisbattery supplying current to operate the receiving relay R at station P.The circuit operating relay R. includes the armature and marking contactin of relay S, the upper winding of relay R, the armature and markingcontact of relay C, the lower winding of relay R. and ground. Thecurrent traversing the upper winding of the receiving relay R1 will begreater than the small holding current emanating from battery B1and-traversing resistor Z1 and the lower winding of the receiving relayR. The current received will therefore act to move the armature of thereceiving relay R to its spacing contact,

Upon the closure of the spacing contact s of the receiving relay R,battery B2 will oppose battery 3'0 and no current will flow over thecircuit including, in addition to spacing contact s and armature of therelay R, the upper windings of the relays S and C, the resistor Z'z andthe loop circuit L1 to which the sounder Q is connected. This sounderwill register a spacing signal. It will be seen therefore that theapparatus at stations P and P will relay signals between the loopcircuits L1 and L1. Relay S and C will be held on their marking contactsby a current which flows from battery B'2 through the lower windings ofthese relays.

The closure of the spacing contact 5 of the control relay C at station Pwill disconnect ground from the marking contact m of relay S, thisgrounded connection having previously been established through the upperwinding of relay R, the armature and marking contact of relay C and thelower winding of relay R. At the same time the battery BTl will besubstituted for ground at the marking contact m of relay S, theinterconnecting circuit including the upper winding of relay R inaddition to the armature and spacing contact s of relay 0. Hence theclosure of the spacing contact s of relay C will produce a situation inwhich the armature of the sending relay S will move between two contactswhich are connected to equal and oppositely poled batteries B11 and B12.

If now a marking signal is transmitted over the subscribers loop circuitL1, as for example, by closing the contact m of key K, the current nowtraversing the upper windings of relays C and S will be such as to tendto move the armatures of these relays to their marking contacts m. Therelay S, being of the fast-releasing type, will move its armature to itsmarking contact 111. immediately after the marking signal is impressedupon the system. However, the relay C, which is of the slow releasetype, will require a delay of a substantial time interval as, forexample, 200 milliseconds, before its armature will return to itsmarking contact m. Hence before the relay C has released, the markingbattery B11 will remain connected to the marking contact m of thesending relay S through the upper winding of the relay R, and thereforemarking current will be transmitted over the line L. This markingcurrent will flow over a circuit at station P which includes thearmature and marking contact m of relay S, the upper winding of relay R,the armature and marking contact m of the relay C, the lower winding ofrelay R and ground. This current will cause the armature of thereceiving relay R to promptly close its marking contact 'In. A markingsignal will then be sent over the subscribers loop circuit Li to operatethe sounder Q. This signal will be relayed over a circuit which includesthe battery B1, the marking contact m and armature of relay R, the upperwindings of relays S and C, the resistor Z'z and the loop circuit L1,which includes the sounder Q. The sounder Q will, of course, registerthe marking signal. Relays S and C' will be held on their markingcontacts by a current which flows from battery B'1 through the lowerwindings of these relays.

It has been assumed that the marking signal transmitted over thesubscribers loop circuit L1 to the station P was not of sufilcientduration to cause relay C to return to its marking contact. If, however,the marking signal has exceeded the releasing time of relay C, thearmature of relay 0 will have returned to its marking contact m. Thenupon the closure of the contact m of relay C, the marking contact ofrelay S will be reconnected to ground. The grounded connection will bere-established over a circuit including the upper winding of relay R,the armature and marking contact m of relay C, the lower winding ofrelay R and ground. Thus the circuit will be restored to the conditionformerly prevailing when it was idle. The apparatus at station P is nowready to receve signals coming from station P.

If marking and spacing signals are transmitted in rapid succession overthe subscribers loop L1 to the apparatus of station P before the relay Chas released its armature to its marking contact m, then the battery B11will be continuously connected to the marking contact 111. of relay Sthrough the upper winding ofthe relay R. These marking and spacingsignals will be relayed over the line L as the armature of relay S movesback and forth between its marking and spacing contacts m and s.Moreover, the movement of the armature of relay S between the twooppositely poled batteries B11 and B12 will cause substantial oppositelydirected currents to traverse the windings of the receiving relay R andconsequently the armature of relay R will move between its twocorresponding contacts m and s in accordance with'the signals. Theapparatus of station P will then relay the same signals over' the loopcircuit L'i to the sounder Q.

It will be noted that after the telegraph system of Fig. 1 has been idlewith substantially no current in the line L and a spacing signal isthereafter transmitted over the line, the line current will change froma zero value to a large spacing value. This current will be obtained, asalready explained, from the battery B12 at station P and it willtraverse the windings of the receiving relay R at station P to operatethat relay. This current change is in contrast to subsequent currentchanges forcorresponding spacing signals in which the current changesfrom a large value for a marking signal to an oppositely directedsubstantially equally large value for a spacing signal. The initialspacing signal will therefore be somewhat abnormal and distorted.

Fig. 3 graphically illustrates this condition. The marking current isillustrated as approximately equal and opposite to the spacing current.The change from the marking condition to the spacing condition is shownby the curve drawn through the point Y. But in the system of Fig. 1, thefirst spacing impulse follows the idle condition of the circuit in whichno current is in the line. The growth of current in the line-of Fig. 1during the first spacing signal is shown by the curve drawn through'thepoints 0 and-X.

It will be observed that if the ordinate of the point Y corresponds tothe current required to operate the armature of the receiving relay toits spacing contact after a-marking signal was received, the abscissa ofthe point Y will measure the time which must elapse before the spacingsignal will be eirective in the relay. The first spacing impulse in theFig. 1 system, however, will operate the receiving relay after a brieferinterval of time which is measured by the abscissa pf the point-X-.- Thediii'erence between these two intervals results in signal distortion.The circuit of Fig. 1 may nevertheless be employed for telegraphtransmission where such distortion may be tolerated.

The distortion just referred to may be obviated by delaying theoperation of the sending relay S of station P. That is, with the receiptof the first spacing impulse from the loop circuit L1, the relay C willoperate to close its spacing contact s before the relay S will beoperated to its spacing contact 8. Thus, the marking battery B11 will beconnected to the line L through the upper winding of the relay R beforethe spacing battery H12 will be connected to the line L. The operationof the relay C will first cause a large current corresponding to amarking signal to flow over the line L, and the subsequent operation ofthe relay S will cause a reversal of the current to correspond to aspacing condition. This will entail some delay in the transmission ofthe first spacing signal. However, the delay will be substantially thesame as the delay for any subsequent spacing signal. There will,therefore, be no appreciable distortion in the signals. A circuitsuitable for eliminating signal distortion in a-tWo-way, one-pathtelegraph system is illustrated in Fig. 2.

In the circuit of Fig. 2 the repeater apparatus at station P includestwo sending relays S1 and S2, the relay S2 being controlled by the relayS1, as will be explained hereinafter. This repeater also includes aholding relay H and a break relay K. During the idle condition of theFig. 2 circuit, the armatures of all of the relays at both of therepeater stations P and P will be on their marking contacts, as shown inthe drawing, and the loop circuits L1 and U1 will be closed. The line Lwill be connected to ground at each end. The connection to ground atstation P will be completed through a circuit including the armature 2and marking contact m of relay H, the armatur and marking contact m ofrelay S2, the resistor Z11, the upper winding of relay R, the armature Iand marking contact m of relay H, the armature and marking contact m ofrelay C, the lower winding of relay R and ground. A similar circuit forgrounding the other end of the line L will be completed at station P. Nocurrent will then be transmitted over the line L.

A spacing signal may be transmitted by opening the loop circuit L1 atthe key K. When this happens the relays S1 and C will close theirspacing contacts simultaneously. The operation of the relay C willconnect the spacing battery B2 to the line L over a circuit whichincludes the coil W1, the spacing contact s and armature of relay 0, themarking contact m and armature I of relay H, the upper winding of relayR, resistor Z11, marking contact m and armature of relay S2, and themarking contact 111. and armatur 2 of relay H to the line L. Thusmarking current will be transmitted over the line L. The receiving relayR at station P will, however, maintain its armature on its markingcontact where it previously was.

The closure of the spacing contact of relay C will also operate theholding relay H to its spacing contacts 5. The circuit for operating therelay H will include, in addition to the battery E2, the winding W1, thespacing contact s and armature of relay C, the winding of relay H,resistor Z12 and ground. The operation of the relay H will then open ashunt circuit around a noise killer comprising a coil W2 and a resistorZ13,

the shunt circuit having been previously established by the closure ofthe right-hand marking contact m of relay H by its armature 2. Theoperation of the relay H also substitutes the battery B2 connected toits left-hand spacing contact 8 for the battery B2 formerly connected tothe spacing contact .9 of the relay C. The new battery is now connectedto the line L over a circuit which includes the spacing contact s andarmature I of relay H, the upper winding of relay R, the resistor Z11,the marking contact m and armature of relay S2, the resistor Z13, andthe coil W2 to the line.

The operation of the relay S1 to its spacing contact s will also causethe operation of the relay S2 to its spacing contact 8 after the lapseof a predetermined time interval. The operating circuit for relay S2will include the battery B1 connected to the spacing contact of relayS1, the armature of relay S1, the two equal resistors Z10, the lowerwinding of relay S2 and ground. The resistors Z10 have their commonterminal grounded through a condenser K1'0. The resistors Z10 and thecondenser K10 comprise a delay circuit which allows the relay S2 tooperate a predetermined interval of time after the relay S1 hasoperated. Additional delay in the operation of relay S2 is obtained byshortening the upper winding of relay S2. The constants of the delaycircuit may be changed as desired and the delay may, for example, be 15milliseconds. This delay circuit is interposed between the two sendingrelays S1 and S2 for delaying the operation of relay S2 according to oneof the primary features of this invention.

After the spacing contact 8 of the relay S2 is closed, the spacingbattery B1 willbe connected to the line L through the armature of relayS2, the resistor Z1: and the coil W2. The latter battery will send aspacing current over the line L to the repeater station P. It will benoted that the spacing battery B1 will be connected to the line L inresponse to a spacing signal only after the marking battery B2 haspreviously been connected to the line.

The receipt of the spacing current at station P will cause the receivingrelay R to close its spacing contact 5. The circuit for so operating therelay R will include the line L, the armature 2 and marking contact inof relay H, the armature and marking contact 'm of relay S2, theresistor Z'11, the upper winding of relay R, the armature I and markingcontact m of relay H, the armature and marking contact m of relay C, thelower winding of relay R and ground. It will be observed that thespacing current will flow through the two windings of relay R which areefiectively connected in series with each other.

In response to the closure of the spacing con tact s of relay R aspacing signal will be transmitted to the subscribers loop circuit L1,the interconnected circuit including battery B1 connected to the markingcontact of relay S1, the armature of relay S1, the spacing contact 8 andarmature of relay R, the upper windings of relay C and S1, the resistor2'9, the winding of the sounder Q, the key K, the battery B'1 andground. The sounder Q will register the spacing signal.

A marking signal may be transmitted to the distant subscribers stationby closing the loop circuit L1. When the loop circuit L1 is closed, therelays S1 and C will operate to close their marking contacts msimultaneously. The relay H, which is of the slow-release type, willremain on its spacing contacts .9 during the time required for the relayH to become released. This interval may be, for example, 200milliseconds. Relay S2 will be operated in response to the operation ofthe relay S1 after a predetermined dela determined by the constants ofthe network formed by resistors Z and condenser K10, a delay which maybe of the order of milliseconds, as already explained. The operation ofthe relay S2 will cause a marking current to be transmitted over theline L, the circuit completed by the operation of relay S2 including thebattery B2 connected to the left-hand spacing contact of relay H, thearmature I of relay H, the upper winding of relay R, the resistor Z11,the marking contact m and armature of relay 5-2, the resistor Z13 andthe coil W2, which is connected to the line L.

In. response to the received marking current,

rela R at station P" will return its armature to its markin contact m.The circuit now completed at station P will include the line L, thearmature 2 and marking contact m of the relay H, the armature andmarking contact m of the relay S'z, the resistor Z'11, the upper windingof the relay R, the armature l and marking contact m of relay H, thearmature and marking contact m of relay C, the lower winding of relay Rand ground. A marking pulse will then be relayed to the loop L'1 over acircuit including battery B'z, the winding of relay K, the markingcontact m and armature of relay R, the upper windings of relays C andS1, the resistor Z9 and the loop L'1. The sounder Q will then registerthe marking signal.

If, after the last marking impulse, the subscribers loop circuit L1remains closed longer than a predetermined time interval, as, forexample, 200 milliseconds, then the slow release relay H will return itsarmatures to their marking contacts m. When this happens the line L willbe re-connected to ground over a circuit which includes the armature 2and marking contact 122 of relay H, the armature and marking contact 122of relay S2, the

resistor Z11, the upper winding of relay R, the 1 armature I and markingcontact m of relay H, the armature and contact m of relay C, lowerwinding of relay R to ground. It will be noted that the return of thearmature 2 of relay H to its marking contact m has replaced the shuntcircuit around the noise killer W2-Z13. The apparatus at station P willnow be ready to receive signals arriving from the opposite direction.

On the other hand, if the loop circuit L1 remains closed for a periodwhich is less than the predetermined interval of, for example, 200milliseconds, relay H will remain operated to maintain its spacingcontacts s closed. At the same time the marking contact of the relay S2will continue to be connected to the marking battery B2 over a circuitwhich includes the resistor Z11, the upper winding of relay R, thearmature l and spacing contact s of relay H, battery B2 and ground. Thearmature of relay S2 will then continue to travel back and forth betweenits marking and spacing contacts to connect equal and opposite batterypotentials to the line L for the purpose of transmitting marking andspacing signals.

If while signals are being sent from the subscribers loop circuit L1 thesubscriber at loop circuit L'1 desires to break the transmission, thelatter subscriber will open his loop circuit. After a predeterminedperiod, relay K will release since the current previously flowingthrough the upper windings of relays C and S1 through the winding ofrelay K has now been interrupted. Relay K then operates to its spacingcontact. Although current continues to flow through the winding of relayK, the relay adjustment is such that it will agree to spacing.

After the loop L'1 has been opened to transmit the break signal, therelays 8'1 and C will close their spacing contacts s after the relay Rhas returned to its marking contact m. The relays S'i and C'z will closetheir spacing contacts because the current traversing their lowerwindings from battery B'z is spacing in its direction. The closure ofthe spacing contact of relay C will connect battery B1 to the line Lover a circuit which includes the spacing contact s and armature ofrelay C, the marking contact m and armature l of relay H, the upperWinding of rela R, the resistor Z11, the marking contact and armature ofrelay 8'2, the marking contact m and armature 2 of relay H to the lineL.

The closure of the spacing contact of relay C" will also cause relay Hto close its spacing contacts, the circuit operating the relay Hincluding the battery B1, the spacing contact 8 and armature of relay C,the winding of relay H, the resistor Z1z and ground. The closure of theright-hand spacing contact s of relay H will act to substitute thebattery B1 connected to this spacing contact s of relay H for thebattery B1 connected to the spacing contact of relay C". Thus thecircuit now connected to the line L will include the battery B1, thespacing contact and armature l of relay H, the upper winding of relay-R,resistor Z11, the marking contact m and armature of relay Sz, themarking contact 112 and armature 2 of relay H, to the line L. Closure ofthe left-hand spacing contact s of relay H will at the same time removethe shunt around the noise killer W'z and Zn.

The operation of the relay S1 to its spacing contact will also operatethe relay S'z to its spacing contact after a predetermined time intervaldetermined by the constants of the delay circuit Z1oK1o. The closure ofthe spacing contact of relay S'2 will connect spacing battery Bz to theline through the noise killer 2'13 and W'2.

This will cause the receiving relay R at station P to be operated toclose its spacing contact s. In this connection it will be noted thatthere are several currents jointly effective on the windings of therelay R at station P. One of these currents coming from battery B'z ofstation P, will be sent through the upper winding of relay R over acircuit which includes the armature and marking contact of relay S2,resistor Z11, the upper winding of relay R, the armature I and spacingcontact of relay H, battery B2 and ground. Another current will betransmitted through the lower winding of relay R, this current alsoemanating from battery B2. The circuit for supplying the latter currentmay be traced over line L, the armature 2 and spacing contact of relayH, resistor Z18, the marking contact and armature of relay K, the lowerwinding of relay R and ground. Still another current will be obtainedfrom the local battery B1 and this current will flow through the lowerwinding of relay R over a circuit which includes the battery B1, thewinding of relay K, the marking contact and armature of relay R, theresistor Z16, the lower winding of relay R and ground. The combinedeffect of all of these enemas currents will cause relay R to close itsspacing contact s, as already pointed out.

When the spacing contact s of relay R, is thus closed, battery B2 willbe applied to the distant subscribers loop L1 over a circuit whichincludes battery B2, marking contact m and armature of relay S1, thespacing contact and armature of relay R, the upper windings of relays Cand 51, the resistor Z9 and the loop L1. The sounder Q will therefore bereleased and the subscriber will receive the break signal.

It is to be noted that both of the receiving relays It and R are held ontheir previously made contacts by a holding circuit. Current will alwaysflow through the lower windings of the two receiving relays and thiscurrent will be in such a direction as to hold the armature of theserelays on their previously made contacts.

Should an accidental spacing hit arrive at station P from line L, forexample, the relay R might be caused to close its spacing contact s.This is promptly rectified by the circuit of this invention whichincludes an auxiliary break relay K included for this purpose. After apredetermined delay such as 150 milliseconds, the relay K will close itsspacing contact. When this happens, battery of proper polarity will beapplied to the windings of the receiving relay R to restore its armatureto its associated marking contact.

Ihe two-way one-path telegraph circuit above described includes tworepeater stations P and. P for interconnecting two loops L1 and U1. Itwill be clear that any pair of similar repeater stations may beinterposed between any two different subscribers loo-p circuits.

The constants referred to hereinabove have been given only for thepurpose of explaining the operation of the system. It will be understoodthat any other constants may be employed in the practice of thisinvention.

While this invention has been shown and de-- scribed in certainparticular arrangements merely for the purpose of illustration, it willbe understood that the general principles of this invention may beapplied to other and widely varied organizations without departing fromthe spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a half-duplex telegraph repeater interconnecting a loop and aline, the combination of a receiving relay, a sending relay, meansresponsive to signals transmitted from the loop to operate the sendingrelay in accordance with the transmitted signals, means responsive tosignals received from said line to operate the receiving relay inaccordance with said received signals, and means for grounding said linea pretermined interval of time after the termination of signaling.

2. In a telegraph system, the combination of a line over which markingand spacing pulses may be transmitted, means for producing substantiallyequal but opposite currents corresponding to marking and spacing pulsesfor transmission over said line, and means responsive to the firstspacing pulse to transmit current corresponding to the marking pulseover said line and for subsequently transmitting current correspondingto the first spacing pulse over said line.

3. In a telegraph system, the combination of a line interconnecting twosubscribers loops over which no current is transmitted when both loopsare idle, means for transmitting equal and opposite currentscorresponding to marking and spacing signals from one loop to the otherover said line, and means responsive to the first spacing signal totransmit current over said line corresponding to a marking signal, saidlatter means including means to delay the transmission over said line ofcurrent corresponding to all signals.

4. In a telegraph system, the combination of a line, two loop circuits,two repeaters connecting said loop circuits with said line, means forsending marking and spacing signals from one loop circuit to the otherloop circuit through said repeaters and over said line, each repeaterinclulding means for delaying by a predetermined time interval the firstspacing signal to be transmitted by said repeater over said line, andmeans for transmitting over said line a current corresponding to amarking signal during said predetermined time interval.

5. In a telegraph system, the combination of a subscribers loop, a line,a repeater connecting said loop and said line, said repeater includingmeans responsive to the first spacing signalv received from said loopfor transmitting over said line during a predetermined time interval acurrent corresponding to a marking signal and for delaying the firstspacing signal by said predetermined time interval, said repeater alsoincluding means for relaying all signals received from said line to saidloop substantially without delay.

6. A telegraph repeater for interconnecting a loop and a line,comprising a first sending relay connected to said loop, a delay networkhaving a predetermined time interval, a secand sending relay controlledby said first sending relay through said delay network, a receivingrelay, said second sending relay and said receiving relay beingconnected to said line, means responsive to signals received from saidline for operating the armature of said receiving relay between itscontacts for relaying said received signals to said loop, said firstsending relay being controlled by currents transmitted from said loop,means responsive to the first spacing signal transmitted from said loopfor operating said second sending relay for transmitting to said line acurrent corresponding to a marking signal for an interval correspondingto the time constant of said delay network, and means for operating saidsecond sending relay after the expiration of said time interval fortransmitting a current corresponding to the first spacing signal oversaid line.

JAMES T. NEISWINTER.

